Award: OCE-1234449

Intellectual Merit. Predators control communities by their direct interactions with prey, which indirectly affects a variety of other species in the network. Chemical cues released into the environment frequently are important in this process by informing prey species about the predator presence and activity. This project examined how the environment and chemical signal properties determine the strength and nature of predator control in an important salt marsh community, where blue crabs prey on mud crabs that prey on oysters. Blue crab predators can increase oyster abundance by both consuming mud crabs and because mud crabs sense blue crabs chemically and stop foraging. This project determined that both water flow and chemical properties strongly affect this process. In areas and times where measured currents are slow and non-turbulent, mud crabs perceive blue crabs from distances of 1-several meters and mud crab foraging is strongly depressed so that oyster abundance is increased. In stronger and more turbulent flows, mud crabs no longer easily perceive blue crab predators. Blue crabs can then consume mud crabs but oysters still are consumed at moderate levels. High levels of fluid flow physically depress mud crab foraging and predation on oysters is low. Thus, the physical environment not only controls the intensity of cascading predator effects, but also whether predators exert these effects by consuming their prey (consumptive effects) or changing prey behavior (non-consumptive effects). Results indicate that blue crabs release urine that is sensed by mud crabs, and that blue crab urine is more potent when blue crabs have consumed mud crabs as opposed to other prey. Chemical analysis of urine via a novel metabolomics method indicates it is a complex mixture composed of common primary metabolites from digestion. Urine from animals fed different diets has the same molecules but present in different concentrations. Two molecules, homarine and trigonellene differ substantially in urine from blue crabs fed mud crabs vs. other items, and explain different potency. Mud crabs respond to homarine and trigonellene (when presented at concentrations in urine) as they do to the raw urine. Homarine and trigonellene likely are produced by many different predators because they are basic metabolites, suggesting they are sensed by other prey species. Initial results suggest oysters also sense these two molecules and respond by creating stronger shells. Broader Impacts. The important molecules identified in this study may provide oyster management and conservation options by their ability to reduce mud crab predation on oysters, and potentially, by increasing oyster resistance to predation. This also may provide ways to increase the productivity of oyster mariculture. This proposal resulted in the development of metabolomics methods to analyze complex chemical blends that may be widely applicable. The project also developed novel methods to examine wave contributions to fluid flow properties that might be useful for other applications. Human resource development of this project includes the training 5 PhD students (one student from underrepresented groups) in chemistry, fluid physics and biology so that they can address problems at the intersection of these fields. Three PhD dissertations were/will be produced. Eight undergraduate students received training (2 underrepresented students), with 2 of them now attending graduate school in related fields. Doctoral students involved in this project performed outreach at inner city K12 schools. This project resulted in a middle school science module presenting biological concepts, data manipulation and graphing, and the scientific method. Last Modified: 11/18/2018 Submitted by: Marc J Weissburg